The brake system serves for decelerating the motor vehicle, thus in this regard, supplying a brake force acting on several wheels of the motor vehicle. The brake force is imposed on the wheels by means of the wheel brakes, i.e., the first wheel brake and the second wheel brake. In this case, the first wheel brake for imposing the brake force is provided on a first of the wheels and the second wheel brake for imposing the brake force is provided on a second of the wheels. If the motor vehicle has more than two wheels, then the brake system preferably has an additional wheel brake for at least one of these other wheels or each one of all the other wheels, by means of which the brake force can also be imposed on the at least one wheel. For example, an actual brake pressure will be applied to the wheel brakes when an operating element is actuated. In this regard, the brake system is present as service brake of the motor vehicle or at least forms a component of the service brake.
The brake system, for example, provides a brake master cylinder, in which a primary brake piston is displaceably arranged. The primary brake piston together with the brake master cylinder limit a reservoir of brake fluid, which is variable, wherein its size depends on the position of the primary brake piston. The primary brake piston is coupled to an operating element, which is present, for example, as brake pedal. By way of the operating element, a driver of the motor vehicle can adjust a desired brake force, which is designated below as pre-specified brake force and is preferably firmly associated with a pre-specified brake pressure.
The brake system is preferably present as an electro-hydraulic brake system. This means that the brake fluid present in the brake fluid reservoir supplies, but does not do so directly, the actual brake pressure applied at the first wheel brake and/or second wheel brake when the operating element is actuated, or in any case supplies a part of it, in at least one mode of operation of the brake system. Rather, a target brake pressure is determined when the operating element is actuated, wherein this can be provided with the use of at least one sensor, which is assigned to the operating element and/or to the primary brake piston and/or to the brake master cylinder and/or to a simulator cylinder at which a simulator piston is displaceably arranged.
For example, the sensor can be designed as a displacement sensor or as a pressure sensor. In the first-named case, the actuation range of the operating element by which the operating element is displaced when it is actuated is determined with the use of the sensor. Additionally or alternatively, of course, the pressure present in the brake master cylinder can be determined by means of the sensor. The target brake pressure is subsequently determined from the values that are measured with the use of the sensor, thus, for example, the displacement and/or the pressure. Then an actual brake pressure that corresponds to the target brake pressure is applied or adjusted at the first wheel brake and/or second wheel brake.
In this case, the actual brake pressure is supplied by the brake pressure source, which is present, for example, in the form of a pump, in particular, an electrically operated pump. In the above-described mode of operation of the brake system, in this regard, the brake fluid reservoir is not, or at least is not directly, connected or fluidically connected to the first wheel brake and/or second wheel brake. However, in order to provide haptic feedback to the driver of the motor vehicle when the operating element is actuated, an—optional—brake force simulator is preferably assigned to the brake master cylinder. The latter comprises the simulator piston, which is arranged displaceably in a simulator cylinder and supported at a wall of the simulator cylinder via a spring element, and in this respect is filter-force-loaded.
The simulator piston together with the simulator cylinder limit a simulator fluid reservoir, which is variable, analogous to the brake fluid reservoir, wherein the size of the simulator fluid reservoir depends on the position of the simulator piston. The simulator fluid reservoir is fluidically connected to the brake fluid reservoir. When the operating element is actuated, the brake fluid reservoir is reduced and brake fluid present in the brake fluid reservoir is conveyed to the simulator fluid reservoir. Correspondingly, the simulator fluid reservoir increases, whereby the simulator piston is deflected against the spring force.
Depending on the spring force, which may depend on the deflection of the simulator piston, a counter-force acts on the operating element in the described mode of operation, due to the flow connection between the simulator fluid reservoir and the brake fluid reservoir, and this counter-force is directed against an operating force applied to the operating element by the driver of the motor vehicle. Correspondingly, the driver receives haptic feedback by way of the operating element, and this feedback is essentially dependent on the deflection of the operating element from its initial position or resting position.
To supply a fallback level in case of a defect in the brake system, for example, when a failure of the brake pressure source occurs, preferably a direct flow connection is present between the brake master cylinder and the first wheel brake and/or second wheel brake. In this way, even in case of a defect in the brake system, when the operating element is actuated, an actual brake pressure can be built up at the first wheel brake and/or second wheel brake. For this, however, the driver must apply an essentially greater operating force than usual on the operating element.
The first inlet valve, the first outlet valve, and the first separating valve are fluidically assigned to the first wheel brake. Thus, the first inlet valve and the second outlet valve are each fluidically connected on one side at the first wheel brake. On its side turned away from the first wheel brake, the first inlet valve is connected fluidically at the first separating valve, thus at an output side of the first separating valve.
The input side of the first separating valve, which is fluidically turned away from the wheel brake, is preferably fluidically connected at the brake master cylinder or the brake fluid reservoir, and/or the brake pressure source. The side of the first outlet valve, which is turned away from the first wheel brake, in contrast, is preferably fluidically connected at a supply reservoir, and/or the brake master cylinder, and/or the brake pressure source.
To build up the actual brake pressure at the first wheel brake, the first separating valve and the first inlet valve are opened, so that brake fluid can flow from the brake master cylinder and/or the brake pressure source in the direction of the first wheel brake. After the build-up of the actual brake pressure, the first inlet valve and/or the first separating valve can be closed—when the first outlet valve is closed. Correspondingly, the actual brake pressure of the first wheel brake is kept constant. In order to dissipate the actual brake pressure of the first wheel brake, the first outlet valve is opened. The brake fluid previously guided to the first wheel brake can flow via the latter first outlet valve in the direction of the supply reservoir, the brake master cylinder, and/or the brake pressure source.
The second inlet valve, the second outlet valve, and the second separating valve are assigned to the second wheel brake. The designs for the first wheel brake and the valves assigned to the latter are drawn on analogously for the second wheel brake, wherein the second inlet valve corresponds to the first inlet valve, the second outlet valve corresponds to the first outlet valve, and the second separating valve corresponds to the first separating valve.